diff --git a/src/region_plane.cpp b/src/region_plane.cpp
index 5917efc11b..6dc162eead 100644
--- a/src/region_plane.cpp
+++ b/src/region_plane.cpp
@@ -27,6 +27,8 @@ using namespace LAMMPS_NS;
 RegPlane::RegPlane(LAMMPS *lmp, int narg, char **arg) : Region(lmp, narg, arg),
     xstr(nullptr), ystr(nullptr), zstr(nullptr)
 {
+  xvar = yvar = zvar = 0.0;
+
   options(narg - 8, &arg[8]);
 
   if (utils::strmatch(arg[2], "^v_")) {